The present invention relates to semiconductor lasers and, more particularly, to a high-power, single-mode pump laser having a widened gain medium, increased optical power, reduced laser junction temperature, and a stabilized operating spectrum.
Semiconductor pump lasers have become indispensable components in modem fiber-optic communication systems and networks. In response to the ever-increasing demands placed on those systems and networks by the Internet, for example, Dense Wavelength Division Multiplexing (DWDM) has emerged as the communication protocol of choice; with a channel capacity in excess of eighty (80) channels. However, more channels require greater laser pumping power. For example, an eighty-channel DWDM system may require two 980 nm lasers and four 1480 nm lasers, each producing 150 mW of output power. For a Raman amplifier, more than four conventional lasers may be required. This not only increases the size of the system, but also makes the control circuits very complex. It is thus desirable to increase the pump power of a laser sufficient to eliminate the need for multiple lasers, i.e., to design a single laser with sufficient pump power and without increasing the laser junction temperature.
Laser power may be increased by increasing the chip length, thereby increasing the gain volume. That solution, however, is limited by the internal loss of the waveguide. Another solution is to increase the width of the active gain region. Unfortunately, that introduces a second transverse mode into the laser signal. Yet another solution requires the use of a master oscillator power amplifier structure. The complexity of the fabrication process and the difficulty in coupling light into a single mode fiber render that solution undesirable.
There thus exists a need in the art for a high-power laser that overcomes the above-described shortcomings of the prior art.
The present invention is directed to a large area single-mode (LASM) laser system that provides a laser having a wider gain medium and thus a higher power output without introducing the second transverse mode into the optical signal. The laser system of the present invention also reduces the laser junction temperature, thereby improving the reliability of the laser and of laser systems constructed therefrom. The present invention also provides a stabilized spectrum in an optical signal by providing a means for feeding back to the laser only a single mode of an optical signal generated by the laser.
The present invention is directed to a large area single-mode (LASM) laser system comprising a laser having a gain region of predetermined area defined by a generally horizontal gain width and generally vertical waveguide width and including a gain medium. The laser is preferably operable in spontaneous emission mode and causes an optical signal to propagate from the laser in a propagation direction. The LASM laser system also includes an optical signal conditioner located downstream from the laser in the propagation direction. The optical signal conditioner reflects a single mode of the optical signal in a direction opposite of the propagation direction and facilitates single-mode operation of the laser.
In another embodiment of the present invention, a large area single mode (LASM) laser system comprises a laser having a gain region of predetermined area defined by a generally horizontal gain width and generally vertical waveguide width and including a gain medium. The laser is preferably operable in spontaneous emission mode and causes an optical signal to propagate from the laser in a propagation direction. The LASM laser system of this embodiment also includes a first lens located downstream from the laser in the propagation direction for focusing the optical signal in a generally vertical direction with regard to the gain region and in a direction opposite of the propagation direction. The LASM laser system further includes a second lens located downstream from the first lens in the propagation direction and for collimating the optical signal in a generally horizontal direction and in a generally vertical direction, with regard to the gain medium. The LASM laser system additionally includes a single-mode fiber-optic cable located downstream from the second lens in the propagation direction and having a fiber grating for reflecting a single-mode of the optical signal in a direction opposite of the propagation direction. The reflected single-mode of the optical signal facilitates single-mode operation of the laser.
In yet another embodiment of the present invention, a large area single-mode (LASM) laser system comprises a laser having a gain region of predetermined area defined by a generally horizontal gain width and generally vertical waveguide width and including a gain medium. The laser is preferably operable in spontaneous emission mode and causes an optical signal to propagate from the laser in a propagation direction. The LASM laser system of this embodiment also includes a tapered fiber-optic system located downstream from the laser in the propagation direction and that has a cylindrical lens at an optical input of the tapered fiber-optic system, and a tapered fiber core optically coupled to a single-mode fiber-optic cable including a fiber grating for reflecting a single-mode of said optical signal in a direction opposite of the propagation direction. The reflected single-mode of the optical signal facilitates single-mode operation of the laser.
Other objects and features of the present invention will become apparent from the following detailed description, considered in conjunction with the accompanying drawing figures. It is to be understood, however, that the drawings, which are not to scale, are designed solely for the purpose of illustration and not as a definition of the limits of the invention, for which reference should be made to the appended claims.